Taking the stand in his trial on endangerment and assault charges, Melvin Morse said that when the girl was about 8 years old, it became a struggle within the household to keep her hair clean.
"Always the problem is soaping up her hair and it gets in her eyes and she doesn't want the water on her hair to get the soap out of it," Morse said.
Morse, 60, said the girl's mother, Pauline Morse, first took on the hair-washing duties but gave up after a couple of months and asked him to do it.
"It pretty much was always a thrash," Morse said. "... The two of them were going at each other, and it just wasn't worth it."
But Morse said he tried no more than four or five times before he, too, gave up.
"I did say to her, 'I'm not waterboarding you.... This isn't some kind of torture,' " he told jurors, using a term that both Pauline Morse and the girl have said he used at home.
Morse said that after the couple talked to friends and gave up on the hair washing, Pauline Morse bought some aromatic bath products for her to use, and "the problem just went away."
The girl, now 12, and her mother have testified that Morse used hair-washing as a threat or punishment when she misbehaved.
Morse could face more than 20 years in prison if convicted on all charges.
Pauline Morse, 41, agreed to plead guilty last year to misdemeanor endangerment charges and to testify against Melvin Morse.
The allegations of waterboarding surfaced after the girl ran away from home in July 2012, the morning after Melvin Morse reportedly grabbed her by the ankle and dragged her across a gravel driveway into the house, where she was spanked and warned of worse punishment the next day.
Morse has denied police claims that he may have been using waterboarding to experiment on the girl. Waterboarding simulates drowning and has been used in the past by U.S. interrogators on terror suspects. Many critics call it torture.
The girl, who only recently the girl found out Morse wasn't her biological father, says the waterboarding left her struggling for breath and was only one of several forms of physical punishment to which Morse subjected her.
Laurel Braunstein, a social worker for the state attorney general's office, testified Monday that the girl told prosecutors in September 2012 that Morse waterboarded her by taking the spray attachment in the kitchen sink and spraying water up her nose, causing her pain.
"She said once or twice she felt like she was going to die," Braunstein said.
Morse described how he and Pauline tried to deal with the behavioral problems of the girl, who was about 4 years old when her mother began living with Morse. Morse testified that at that age, the girl still had not been toilet-trained, ate food out of the garbage can, and still used a pacifier.
But he also described the girl as a talented young, artist and musician, avid reader and honor roll student.
Morse said the girl's behavioral problems worsened after 2007, when she was sexually molested by a female relative, who is also accused of holding the girl by her ankle and trying to drop her from a second-floor stair railing.
Morse said the girl became angry, defiant and often uncooperative after being abused by the relative.
"She certainly was angry at us for not protecting her," he said.
Morse said the primary means of disciplining the girl was "timeouts," in which she had to stand, one minute for every year of age. He acknowledged that the girl could be subject to such treatment several times a day.
"There were days when she seemed to be in trouble all day," he said.
Prosecutors have suggested that the girl was forced to stand for hours at a time with her arms held out and her head against a wall.
The girl and her mother also have said Morse would alternately deprive her of food or force-feed her, and that she was often confined to her room, where she sometimes wet herself or used her closet or toy box as a toilet. They also said she often was isolated from family dinners and activities.
In a statement after his arrest in August 2012, Morse admitted that he once slapped the girl about three years earlier.
On Monday, he said the slapping occurred on a day when he and the girl "were just pushing each other's buttons," and she stuck a finger in her nose.
"I slapped her, I did. Not thinking, I slapped her," said Morse, adding that afterward, the girl put her other finger in her nose. Morse then took a photograph of the tearful girl, which prosecutors have introduced into evidence.
Morse has authored several books and articles on paranormal science and near-death experiences involving children. He has appeared on shows such as "Larry King Live" and the "The Oprah Winfrey Show" to discuss his research, which also has been featured on an episode of "Unsolved Mysteries" and in an article in "Rolling Stone" magazine.
He will resume his testimony on Tuesday.
